Field of the Invention
Embodiments disclosed herein generally relate to an apparatus for fabricating films on substrates in a processing chamber, more particularly, for a substrate support assembly used in a processing chamber to provide non-uniform gas flow for plasma processing applications.
Description of the Related Art
Liquid crystal displays or flat panels are commonly used for active matrix displays, such as computer, television, and other monitors. Plasma enhanced chemical vapor deposition (PECVD) is used to deposit thin films on a substrate, such as a semiconductor wafer or a transparent substrate for a flat panel display. PECVD is generally accomplished by introducing a precursor gas or gas mixture into a vacuum chamber containing a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the processing chamber. The precursor gas or gas mixture in the processing chamber is energized (e.g., excited) into a plasma by applying a power, such as a radio frequency (RF) power, to an electrode in the processing chamber from one or more power sources coupled to the electrode. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate. The layer may be, for example, a passivation layer, a gate insulator, a buffer layer, and/or an etch stop layer. The layer may be a part of a larger structure, such as, for example, a thin film transistor (TFT) or an active matrix organic light emitting diodes (AMOLED) used in a display device.
Flat panels processed by PECVD techniques are typically large. For example, the flat panel may exceed 4 square meters. During a deposition processing, a plasma is generated to form active ions so as to deposit a material layer on a substrate. The plasma may be easily ignited in processing chambers that utilized capacitively coupled power, inductively coupled power, or microwave power to energize the gases forming the plasma. However, the plasma generated in the processing chamber as well as gas flow distribution may often not be uniformly distributed all across an entire surface of the substrate. For example, the plasma or precursor gas flow may not always extend to an edge of the substrate, resulting in different edge to center processing rates. Non-uniform plasma or gas flow distribution at different locations across the substrate surface may result in asymmetrical or non-uniform processing profiles of the target-processing material disposed on the substrate, which may affect the deposition uniformity and defect rates. As such, non-uniform plasma or gas flow distribution across the substrate surface may eventually result in defects, such as feature deformation, non-uniform or irregular feature profile of the resultant material layer formed on the substrate. Furthermore, non-uniform plasma or gas flow distribution across the substrate surface may also affect the cleaning uniformity and efficiency, and may impact removal film deposits, cause flaking or over-clean and erode chamber component during cleaning processes.
Therefore, there is a need for an improved apparatus for controllable plasma or gas flow distribution control across a substrate surface during a plasma process.